An example of a conventional internal combustion engine of a saddle riding vehicle is known, which is provided with a cam chain tensioner device and a cylinder with its axis inclined with respect to a vertical direction, as disclosed in Patent Document 1 below. In the internal combustion engine, a lubricant supply passage to a tensioner lifter of the cam chain tensioner device has an ascending slope. Accordingly, when operation of the internal combustion engine is stopped, lubricant oil returns from the tensioner lifter to a supply source through the lubricant supply passage. For this reason, when the engine is restarted after it is stopped, operability of the tensioner lifter cannot be sufficiently increased until oil is sufficiently supplied to the tensioner lifter. This situation brings about a drawback that noise from the cam chain cannot be reduced mainly because of fluttering of the cam chain that occurs due to the reduced operability of the tensioner lifter.